mlxsw: spectrum_router: Set abort trap for IPv6

When we fail to insert a route we invoke the abort mechanism which
flushes all the tables and inserts a default route in each, so that all
packets incoming to the router will be trapped to the CPU.

Upon abort, add an IPv6 default route to the IPv6 tables.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>